SAT Subject Physics Practice Question 290: Answer and Explanation

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Question: 290

61. A vertically polarized plane wave (an AM radio wave) is emitted by a radio antenna and travels across flat ground. Which of the following could describe the direction of the magnetic field component of the wave?

A. Parallel to the ground and perpendicular to the direction of propagation
B. Perpendicular to the ground and to the direction of propagation
C. Parallel to the ground and to the direction of propagation
D. Perpendicular to the ground and parallel to the direction of propagation
E. Parallel to the electric field component of the wave

Correct Answer: A

Explanation:

By definition, if the wave is vertically polarized, the electric field component, E, of the wave always oscillates vertically. That is, E is perpendicular to the ground. Since the direction of propagation, S, is parallel to the ground, and the vectors E, B, and S are always mutually perpendicular, B must be parallel to the ground and perpendicular to S.

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